Cyn
Cyn cael cinio
Cyn cyrraedd

But i must be used with a person:

Cyn i fi gael cinio. Before I have dinner.
Cyn iddi hi gyrraedd. Before she arrives.

Remember to use the correct suffix with i. You can find the conjugation of the preposition i and other prepositions by clicking here.

There are other words which are used in this way with i, e.g.

Nes, ar ôl, rhag ofn, erbyn,
e.g.
Erbyn i ti gyrraedd ---- by the time you arrive
Ar ôl i chi adael --- after you left

Don't forget that most prepositions cause a soft mutation. A table of mutations can be found by clicking here.